Hold the alabaster plate and carefully wipe off any dust, dirt and small debris using a clean cotton cloth. You can also use a feather duster on your alabaster plate as well.
Inspect your alabaster plate under good lighting and look for stains.
Mix a solution of 3 oz. cream of tartar and 1 oz. hydrogen peroxide in a small bowl.
Dip a cotton cloth or sponge into the solution, ring out and rub the stained areas gently.
Dip half of an unused cotton cloth or sponge in a bowl of clean water. Wipe the areas with the cloth to remove the solution. Use the dry side of the cloth to wipe off any moisture. Set your alabaster plate aside to dry at room temperature before storing or displaying.